The present invention is directed to a novel procedure for preparing ammonia and an ammonia catalyst. In particular, the present invention is directed to the use of a lanthanide promoted Group VIII metal cyanide salt as a catalyst for the production of an ammonia catalyst and a novel method of producing these catalysts. In addition, the lanthanide promoted Group VIII cyanide catalyst may also include an alkali and/or alkaline earth metal as a promoter.
The use of hexacyanate salts of the Group VIII transition metals as precursors for ammonia synthesis catalysts have been known. In addition, the use of alkali or alkaline earth metal salts of the Group VIII metal hexacyanate complexes in particularly Fe, as precursors for ammonia synthesis catalysts has been reported in the patents issued to Clancy (U.S. Pat. Nos. 1,439,291; 1,454,599; and 1,363,392). Moreover, the patents to Johnson et al., U.S. Pat. Nos. 4,348,370 and 4,309,311 are directed to the use of alkali or alkaline earth promoted Fe and Co hexacyanocobaltate and hexacyanoruthenate as catalysts for synthesis of ammonia.
In Chemical Abstracts, Volume 90, 1979, Nos. 157737-157739, the use of rare earth metals in combination with U and/or aluminum and hexacyanoferrate complexes are disclosed as ammonia catalyst. In addition, the use of intermetallic alloys which are based on the combination of a rare earth metal and a Group VIII metal have also been disclosed as suitable for ammonia synthesis catalysts. Such Russian Patent Author Certificate No. 740,274 and the Takeshita et al. article in the Journal of Catalysts, Volume 44, pgs. 236-243.
Recently, EPO Patent Application No. 171,296 (U.S. Pat. No. 4,588,705) was published and discloses a dual colloid catalyst system which may be utilized for the production of ammonia. The dual colloid catalyst of this application is prepared by forming a gel or suspension of a transition metal cyano containing anionic complex and a solution containing metal cations wherein at least one metal is non-reducible and selected from Cr, Al, Th, U, lanthanides and Group IIA. This gel or suspension is then heated in an acidic environment at 90.degree. C. to 150.degree. C. to allow hydrolysis and polymerization to occur forming a precursor which is subsequently activated in hydrogen to produce the active catalyst. Example 5 of this patent application discusses the x-ray diffraction results of this type of catalyst precursor identifying the precursor as small crystallites of a RuRu (CN).sub.6 type material.
While each of these patents or articles teaches catalysts having significant catalytic effect in the production of ammonia from nitrogen and hydrogen they have significant limitations. For example, the rare earth--Group VIII metal catalysts which are based on intermetallic alloys have a significant limitation in that the surface area of the catalysts produced is extremely small. In order to achieve a surface area of even 1 m.sup.2 /g, these intermetallics must be ground to fine particles prior to use. While this technique is suitable for low pressure laboratory experiments such as those carried out in the Russian Patent and the work discussed in the Takeshita paper, it is completely unsuitable for the present day commercial environment because the use of fine powders will lead to undesirable pressure drops in the reactor. Moreover, this grinding technique is quite costly. Finally, the intermetallic alloys are not readily suitable for incorporation of promoters. The catalyst disclosed in Chemical Abstracts article has the attendant disadvantage that they require the presence of U which is not a desired material due to its handling problems. The catalyst disclosed in EPO Patent Application No. 171,296 or U.S. Pat. No. 4,588,705 requires a complex preparation technique including heating in an acidic solution for an extended period of time to produce a dual colloid precursor. This technique is unacceptable from the standpoint of complexity and economics. The present invention is directed to a novel process of producing ammonia and a catalyst preparing ammonia catalyst which substantially alleviates these problems.